The present invention relates to a semiconductor device, and more particularly, to a semiconductor package and a module printed circuit board (PCB) for mounting the same.
In recent years, the spread of multimedia and digital devices has led to the ever-increasing demand for large-capacity small-sized versatile semiconductor products that operate at high speed and consume low power. Thus, finer pitches and higher pins are being increasingly applied to the semiconductor products, so that semiconductor packages are showing a tendency to be replaced by ball grid array (BGA) packages using substrates. The BGA packages include micro BGA packages, wire bonding BGA (WBGA) packages, and board on chip (BOC) packages.
A BGA package is adhered to a substrate using solder balls instead of connecting the package with the substrate using outer leads, and 2 to 32 BGA packages are typically mounted on a single module printed circuit board (PCB).
FIG. 1 is a diagram showing a conventional module PCB 10 for mounting a semiconductor package.
Referring to FIG. 1, the module PCB 10 includes a circuit substrate 12. Mount regions 14 on which semiconductor packages are mounted are disposed on the circuit substrate 12. A plurality of pads 20 are disposed on the mount regions 14 and connected to the semiconductor packages, respectively. The arrangement of the pads disposed on the mount regions 14 may be variously designed according to the type of the semiconductor packages mounted on the mount regions 14. For example, the pads may be arranged in a row on both edges of the mount region 14 as illustrated in FIG. 1, arranged in the center of the mount region 14, or arranged in a matrix shape.
Also, pads are formed in the semiconductor packages in positions corresponding to the pads 20 arranged on the PCB 10. Typically, pads used for the connection of semiconductor packages with a PCB may be classified into solder mask defined (SMD) pads and non solder mask defined (NSMD) pads.
FIG. 2A is a plan view of an NSMD pad 20 and FIG. 2B is a cross sectional view taken along line I-I′ of FIG. 2A.
Referring to FIGS. 2A and 2B, the NSMD pad 20 includes a photo solder resist (PSR) 22, which is coated on a circuit substrate 12 and has an opening 23, and a conductive pad 24, which is disposed on the circuit substrate 12 in the opening 23. In the NSMD pad 20, a sidewall 24e of the conductive pad 24 is spaced a predetermined distance Wa from an edge 22e of the PSR 22 and exposed in the opening 23.
The NSMD pad 20 is highly resistant to a thermal stress because the conductive pad 24 is spaced the predetermined distance Wa from the PSR 22; on the other hand, the NSMD pad 20 is susceptible to a physical stress due to unreliable cohesion of the conductive pad 24 with the circuit substrate 12.
A module PCB on which a semiconductor package is mounted is formed of a flexible material, thus causing the warpage or twist of the module PCB. As a result, a conductive pad may be separated from an NSMD pad or a crack may be made in a circuit substrate that contacts the pad.
FIG. 3A is a plan view of an SMD pad 30 and FIG. 3B is a cross-sectional view taken along line II-II′ of FIG. 3A.
Referring to FIGS. 3A and 3B, the SMD pad 30 includes a conductive pad 34 disposed on a circuit substrate 12 on which a PSR 32 is coated, and the PSR 32 partially overlaps the conductive pad 34. Since a predetermined width Wb of an edge 34e of the conductive pad 34 is covered with the PSR 32, the SMD pad 30 is highly resistant to a physical stress, but a thermal stress is concentrated on a portion of the conductive pad 34 that is in contact with the PSR 32.